We are now studying a group of transplantable tumors in rats, mice and hamsters as part of our effort to evaluate the interactions between the metabolism of cyclic nucleotides and the growth behavior of neoplastic cells. These tumors include melanomas in mice and hamsters, a series of hepatomas in rats and a group of sarcomas and testicular and ovarian tumors in mice. This broad spectrum of tumors provides the necessary range of cell types in which to evaluate current putative generalizations concerning the interactions of cyclic nucleotides with certain parameters of mitotic activity and cell surface properties. Although a number of well documented examples of tumor or tissue culture cell growth inhibition by cyclic nucleotides are pubdished, there are a similarly impressive collection of observations which illustrate very rapid mitotic activity in the presence of elevated levels of cyclic AMP. Our goal then is to try to developed data which will contribute to an understanding of those variables which influence the response of the mitotic behavior of a cell type to the constraining influences of elevated cyclic AMP levels. We will examine cyclic AMP and GMP levels in intact cells. In broken cells we will examine adenyl and guanyl cyclase, cyclic AMP and GMP phosphodiesterase, cyclic AMP and GMP stimulated protein kinase, kinase substrates and phosphoprotein phosphatases.